1. Field of the Invention
The present invention relates to a soft magnetic alloy powder; a compact; a high-performance powder magnetic core for use in choke coils, inductors, and the like; and a magnetic element including the powder magnetic core.
2. Description of the Related Art
Conventionally, powder magnetic cores are generally used as a type of magnetic core for use in inductance elements and the like. An Fe-based soft magnetic metal powder which is a soft magnetic material is usually used as a material for the powder magnetic cores. The Fe-based soft magnetic metal powder contains a material having low electrical resistance and therefore has relatively high core loss even if insulation between particles is enhanced. In recent years, compact inductance elements and the like have been demanded; hence, the powder magnetic cores need to have high electrical resistance and low core loss. Therefore, conventional soft magnetic materials need to be improved. In order to increase the electrical resistance of the Fe-based soft magnetic metal powder, a technique of adding Si thereto has been proposed. However, the hardness of the Fe-based soft magnetic metal powder is increased by the addition of Si and therefore the moldability thereof is insufficient to fabricate the powder magnetic cores. This is unsuitable for practical use.
Many Fe—Ni soft magnetic alloy (so-called permalloy) powders are used as materials, other than the Fe-based soft magnetic metal powder, for the powder magnetic cores. However, the Fe—Ni soft magnetic alloy powders are insufficient to suppress the core loss at high frequency. Therefore, Japanese Unexamined Patent Application Publication No. 2001-23811 (hereinafter referred to as Patent Document 1) proposes means for adding Si, Ge, or Sn, which is a group 14 element, for the purpose of reducing the core loss of the Fe—Ni soft magnetic alloy powders. According to Patent Document 1, the addition of a predetermined amount of a group 14 element such as Si to an Fe—Ni soft magnetic alloy powder increases the electrical resistance thereof.
Japanese Unexamined Patent Application Publication No. 2002-173745 (hereinafter referred to as Patent Document 2) discloses permalloy containing Si. According to Patent Document 2, the influence of oxygen on magnetic properties can be reduced by the addition of Si, which acts as a deoxidizing component. However, Patent Document 2 describes that an excessive amount of Si is harmful to soft magnetic properties and therefore the content of Si is limited to 1% by weight or less. Patent Document 2 also describes that Co may be added to permalloy in order to increase the magnetic flux density.
Japanese Unexamined Patent Application Publication No. 63-114108 (hereinafter referred to as Patent Document 3) discloses that Cr, Si, Cu, or Co is used as an additive element in permalloy. However, the amount of the added additive element is not described therein.
Japanese Unexamined Patent Application Publication No. 2008-135674 (hereinafter referred to as Patent Document 4) disclose an Fe—Ni alloy powder in which the problem with the Fe—Ni soft magnetic alloy powder described in Patent Document 1 or 2 is improved and which contains 1% to 6% by mass Co and 1.2% to 4.5% by mass Si relative to the total mass of Fe, Ni, Co, and Si.
As proposed in Patent Document 1, the addition of a predetermined amount of Si only to the Fe—Ni soft magnetic alloy powder significantly reduces the Curie temperature (Tc) and the saturation flux density (Bs). Such a soft magnetic material is insufficient for practical use because magnetic properties of an inductance element including a powder magnetic core made of the soft magnetic material are reduced at effective operating temperature. The permalloy disclosed in Patent Document 2 is insufficient to suppress the core loss and therefore needs to be improved. Patent Document 4 describes that the problem with the Fe—Ni soft magnetic alloy powder described in Patent Document 1 or 2 can be improved using the Fe—Ni alloy powder which contains 1% to 12% by mass Co and 1.2% to 6.5% by mass Si relative to the total mass of Fe, Ni, Co, and Si. However, in recent years, compact electronic devices and high-frequency power supplies have been widely used. Therefore, inductance elements working well at a high frequency of about several megahertz are demanded. The inventors have investigated the conventional Fe—Ni soft magnetic alloy powders described these documents in detail. As a result, the inventors have found that satisfactory properties cannot be obtained in applications used at a high frequency of about several megahertz. Powder magnetic cores cause reductions in magnetic properties due to corrosion and therefore need to have high corrosion resistance.